One of the conventional cooking processes is to fry food items in a body of boiling fat or cooking oil. Sliced potatoes, zucchini, chunks of fish, chicken, shrimp, and the like, may be cooked in this manner in a relatively short time making the process attractive to a fast food restaurant operation. The continuous use of such deep fat fryers, however, cause the oil to be both depleted and contaminated. Merely adding fresh cooking oil is not sufficient to maintain the cooking oil in usable condition.
Spent cooking oil from a deep fat fryer contains various contaminants. Parts of the food product break off during cooking and remain in the cooking oil. Many food products such as fish, chicken, shrimp, zucchini and mushrooms are coated with a seasoned coating prior to immersion in the cooking oil, and particles of the coating break free from the product and remain in the cooking oil. In addition, fat from the food product itself will comingle with the cooking oil and through continuous use the cooking oil will produce contaminants.
It is customary in fast food restaurants to filter the cooking oil at the end of the day. Larger fryers, such as the gas fired fifty pound fryers in conventional use, are provided with drains, and the spent cooking oil is drained from the fryer through a paper filter and into a container. The paper filter will permit the spent oil to pass through the filter but will filter out most particles to produce a substantially particle free oil which is then pumped back into the fryer. Smaller fryers may simply be dumped through a paper cone supported in a nylon bag, the spent oil being collected in a container and returned to the fryer. Merely filtering the spent cooking oil will not remove contaminants except particulate matter.
Cooking oils may be either animal or vegetable in origin. Historically, pork fat has been rendered to produce a lard or cooking oil. Other types of animal fat also can be used for cooking oil. In recent years, various types of vegetable oils have become widely used, such as soybean, cottonseed, rapeseed, peanut, olive, and palm oil. In addition, fish oil has had wide applications in the food industry.
Many of these oils require processing in order to remove flavoring substances or coloring agents. The removal of free fatty acids is one of the purposes of refining crude oils. Various processes for refining crude oils are described in a paper by T. K. Magg entitled Clay-Heat Refining of Edible Oils presented in September 1972 at a symbosium entitled Processing of Edible Oils, AOCS Meeting, Ottawa, Canada. The basis of refining crude oils described in the Magg paper is to remove free fatty acids by deodorization, but to remove prior to deodorization those substances that interfere with satisfactory deodorization, either by pretreating the crude oil with phosphoric acid and bleaching the crude oil or some other process.
While deodorization is a process which may be carried out readily in an oil processing plant, it is not a process which may be utilized readily by a restaurant. Further, the processes for treating crude edible oils may not be effective on spent edible oils, since contaminants have been introduced into the oil from the substances being cooked and the cooking process. Accordingly, it is an object of the present invention to provide a process for rejuvenating spent cooking oil, and to provide such a process which does not require additional equipment beyond the filters already in use, which is not cumbersome, complicated or costly.
The present inventor has found that spent cooking oil may be rejuvenated by directly adding a filtering media to the spent cooking oil in the fryer. The filtering media contains particles of material which become uniformly distributed in suspension throughout the liquid body of the spent cooking oil, and the particles of filtering media material are effective to absorb contaminants and bleach the spent cooking oil to extend the useful life of that cooking oil. The most effective absorption and bleaching action produced by the filtering media occurs when the cooking oil and filtering media are hot, such as 275.degree. F. The filtering media will assume the same temperature of the cooking oil relatively quickly after being added thereto, and the fryer is maintained in operation for a sufficient period of time to permit the filtering media to substantially complete absorbing of the contaminants in the spent cooking oil and bleaching of the cooking oil.
The present invention also contemplates a new and novel filtering media particularly effective for use in rejuvenating spent cooking oil according to the process outlined above. A blend of silicate compounds is provided to collectively achieve the necessary filtering actions for renewing spent cooking oil. The filtering media contains synthetic amorphous silica with absorbed moisture, synthetic amorphous magnesium silicate, diatomaceous earth and synthetic amorphous silica-alumina. Synthetic amorphous silica through absorption and polar attraction will remove trace metals (ligands), thermal and oxidative polymers, alcohols, ketones, aldehydes, acidic and basic compounds, and miscellaneous residual impurities which cause off-odors, off-flavors, and off-colors in spent cooking oil. Synthetic amorphous magnesium silicate will remove acidic compounds, polar compounds, color and odor bodies through absorption. Diatomaceous earth absorbs color bodies and miscellaneous residual impurities. In addition, diatomaceous earth can be provided in relatively large particle size and particle shapes which will facilitate faster filtration. Synthetic amorphous silica-alumina absorbs polar compounds and volatile compounds such as aldehydes and ketones. Synthetic amorphous silica also is obtainable in relatively large particle size to provide faster filtration. The particle size for diatomaceous earth and synthetic amorphous silica-alumina is 20-25 microns in diameter, synthetic amorphous silica and synthetic amorphous magnesium silicate being considerably finer.
The filtering media described above is also effective in refining other edible liquids, particularly wine. The filtering media may be admixed with wine to absorb and attract undesirable taste constituents and to bleach the wine to improve the color and palatability of the wine.